The evidence of two or three witnesses is required to sustain any charge.
This is common sense on the face of it. When there is a dispute, a disagreement between two people, it is very difficult if not impossible to distinguish between who is right and who is wrong. It is the word of one against the other, A matter of 'he said- she said', and we are more likely to believe the one with the greater authority or position or the one who is closest to us, whether or not he or she is right or wrong.
So, of course, if there are more than two or three witnesses, then there are other eyes, other ears, and other voices to say who is and who is not right and true. But today's Gospel is about far more than settling disputes. Jesus is teaching us that our faith, our belief, our worship is not an individual matter - far from it. To be a believer means to be part of a community, to part of the Church. It means, in a deep sense to be part of the Body of Christ - and he dwells in us because we are part of his Body.
While Christ may always be near to us in our private prayers, it is when two or three or more are gathered in his name that he is most fully present. While the Spirit may guide us to right decisions in our lives, it is the Church in the person of the priest who can bind and loose, who can release us from our sins.
As the Poet John Donne wrote, no man - no person - is an island, entire of itself. All of us are connected together, most especially in the Church, and just as it is only by the word of several witnesses that we can have certainty of the truth, so it is that by the Faith of several witnesses, we receive and share and live the Truth himself.